The present invention relates to a hydraulic system with a feed pump for feeding hydraulic fluid.
Feed pumps usually are employed to supply the suction side of a further hydraulic pump with hydraulic fluid. In this way, cavitations in the hydraulic circuit can be avoided in the case of fast changes in pressure. Feed pumps usually are operated with a relatively low delivery pressure.
A typical hydraulic system with a feed pump according to the prior art is shown in FIG. 5. The hydraulic system comprises a closed hydraulic circuit of a variable displacement pump 1 and a variable displacement motor 2, wherein the variable displacement pump 1 is driven by an internal combustion engine and the variable displacement motor 2 drives a winch 4. The feed pump 5 is connected with both sides of the closed hydraulic circuit via check valves 6, in order to avoid cavitations as a result of pressure drops due to dynamic processes such as the swivelling of the pump, and to redeliver hydraulic fluid in the case of external leakages in the hydraulic circuit. Via a transmission 7, the feed pump 5 likewise is driven by the internal combustion engine 3.
Feed pumps are also used to redeliver the differential amount between the volume on the piston and ring surfaces of the hydraulic cylinder in half-open circuits and to supply the storage pumps in accumulator applications with hydraulic fluid with a certain minimum pressure.
Known hydraulic systems with feed pump often have a relatively poor efficiency of the feed pump 5 due to the high mechanical tugging power of the feed pump 5. With a large feed rate, a large number of pumps or pumps with a large absorption volume are required, which requires a correspondingly large installation space at the transfer gear of the internal combustion engine. Possibly, an additional transfer gear or corresponding drives for the pumps are also necessary.